In the processing and packaging of semiconductor devices, conductive bumps are formed for use in providing electrical interconnections. For example, such bumps may be provided for: (1) use in flip-chip applications, (2) use as stand-off conductors, (3) wire looping applications, (4) test points for testing applications, amongst others. Such conductive bumps may be formed in varying techniques. One such technique is to form the conductive bumps using wire, such as on a wire bonding machine or a stud bumping machine.
Numerous techniques for forming conductive bumps on a wire bonding machine or bumping machine are disclosed in U.S. Pat. No. 7,229,906 (entitled “METHOD AND APPARATUS FOR FORMING BUMPS FOR SEMICONDUCTOR INTERCONNECTIONS USING A WIRE BONDING MACHINE”) and U.S. Pat. No. 7,188,759 (entitled “METHOD FOR FORMING CONDUCTIVE BUMPS AND WIRE LOOPS”), both of which are incorporated by reference in their entirety.
FIG. 1 illustrates an exemplary sequence of forming a conductive bump on a wire bonding machine or bumping machine. At Step 1, free air ball 100a is seated at the tip of bonding tool 102. As will be understood by those skilled in the art, prior to Step 1, free air ball 100a has been formed on an end of wire 100 that hangs below the tip of bonding tool 102 using an electronic flame-off device or the like. Wire clamp 104 is also shown at Step 1 in the open position. As will be understood by those skilled in the art, wire 100 is provided by a wire spool on the machine (not shown). Wire 100 extends from the wire spool through wire clamp 104 (and through other structures not shown) and through bonding tool 102.
After free air ball 100a is formed (prior to Step 1), wire 100 is drawn upwards (e.g., using a vacuum control tensioner or the like) such that free air ball 100a is seated at the tip of bonding tool 102 as shown at Step 1 of FIG. 1. At Step 2, bonding tool 102 (along with other elements of a bond head assembly including wire clamp 104) is lowered and free air ball 100a is bonded to bonding location 106 (e.g., a die pad of semiconductor die 106). As will be understood by those skilled in the art, the bonding of free air ball 100a to bonding location 106 may utilize ultrasonic energy, thermosonic energy, thermocompressive energy, XY table scrub, combinations thereof, amongst other techniques.
After free air ball 100a is bonded to bonding location 106 at Step 2 (where the bonded free air ball may now be termed bonded ball 100b), with wire clamp 104 still open, bonding tool 102 is raised to a desired height. This height may be referred to as a separation height (from viewing Step 3 of FIG. 1, one can see that bonding tool 102 has been raised such that bonded ball 100b is no longer seated in the tip of bonding tool 102). At Step 4, with wire clamp 104 still open, bonding tool 102 is moved in at least one horizontal direction (e.g., along the X axis or Y axis of the machine) to smooth the top surface of bonded ball 100b. Such smoothing provides a desirable top surface for a conductive bump, and also weakens the connection between bonded ball 100b and the rest of the wire to assist in the separation therebetween. At Step 5, bonding tool 102 is raised to another height (which may be referred to as the wire tail height), and then wire clamp 104 is closed. Then at Step 6, bonding tool 102 is raised to break the connection between bonded ball 100b (which may now be termed conductive bump 100c) and the remainder of wire 100. For example, bonding tool 102 may be raised to an EFO height which is a position at which an electronic flame-off device forms a free air ball on wire tail 100d of wire 100.
Forming conductive bumps using such conventional techniques involves certain deficiencies. For example, during the smoothing motions in Step 4, the connection between bonded ball 100b and the rest of the wire is weakened; however, in certain processes the connection may be weakened to the point where the connection breaks prematurely (that is, the connection may separate during the rise to tail height shown at Step 5 prior to the closing of clamp 104). If such a premature separation occurs, the wire tail that is provided for the next free air ball (that is, wire tail 100d) may be short (i.e., a short tail condition). In an attempt to avoid such a problem the smoothing in Step 4 may be reduced such that the connection is not excessively weakened; however, this reduction in smoothing may have deleterious effects in terms of the resultant bump surface. Yet another problem that may result is a long tail, where too much wire is on the wire tail. These problems tend to result in yield loss and inconsistency among the conductive bumps.
Further, forming second bonds on a conventional bump (e.g., such as in an SSB type process) involves certain challenges related to, for example, the compliant nature of the bump and the physical configuration of the top surface of the bump. These challenges tend to result in poorly formed second/stitch bonds and potential short tail conditions.
Thus, it would be desirable to provide improved conductive bumps, and improved methods of forming the conductive bumps.